1. Field of the Invention
This invention details a method and structure for forming a removable interconnect for semiconductor packages, where the connector is adapted to repeatedly change from a first shape into a second shape upon being subjected to a temperature change and to repeatedly return to the first shape when not being subjected to the temperature change, and where the connector can be disconnected when the connector is in its second shape and the connector cannot be disconnected when the connector is in its first shape.
2. Description of the Related Art
Due to the high cost of semiconductors, circuit boards and systems it is desirable to provide for a method to be able to remove a semiconductor module from an assembled circuit board without damaging the board or module and thereby enable field replacement capability. At present, such capability is problematic for organic packages, since the actuation loads required in currently available removable solutions exert forces which are incompatible with the organic module structures.
Existing industry solutions for removable packaging interconnect schemes, such as Land Grid Array (LGA) assemblies, apply substantial stresses to the module being connected. Today's best organic module interconnect solution is the use of Ball Grid Array (BGA) solder connections or solderable leads to make the interconnect. Soldered interconnection schemes are not readily replaceable and factory rework processes are difficult and may impact the reliability of the assembled module, particularly in a Pb-free soldering environment. Pin Grid Array interconnects or BGA sockets do provide for more convenient module replacement but can be expensive and often impart changes to electrical parameters, such as increased inductance, that negatively impact device performance. Moreover, these solutions may not be compatible with 1 mm grid I/O pitch.
The best electrical and manufacturing solution available today is the use of Land-Grid Array (LGA) structures. The LGA provides for an array of electrical contact pads on the bottom of the module which is brought into contact with a second level socket to make electrical connections to the circuit board. The drawback here is, in order to establish reliable connections between the module and circuit board, a substantial force (roughly proportional to the number of module pads) must be applied to the interposer/module assembly. Moreover, this actuation force must be maintained for the functional life of the product. The required actuation force is typically excessive for organic semiconductor packages. The high stresses imposed on the laminate substrate structures can cause reliability concerns associated with resin cracks, warpage, inner plane separation and PTH fractures. It is desirable to alleviate the excessive actuation loads associated with a removable interconnect while maintaining manufacturability, electrical performance, reliability, field reworkability, and reasonable cost.